Effect of rhizodegradation in diesel-contaminated soil under different soil conditions

In order to develop a cultivation technique for the practical use of phytoremediation of diesel-contaminated soil, we evaluated the rhizodegradation of diesel-contaminated soil using Italian ryegrass. Experiments were conducted under two different soil conditions that were expected to reduce the influence of diesel on the plant. Under the first condition, the initial diesel concentration which is expressed in the total petroleum hydrocarbon (TPH) concentration was set to 0.80%. The concentration was almost half the upper limit for the growth of Italian ryegrass. Under the second condition, zeolite was added to the experimental soil to improve the cation exchange capacity (CEC). In 152 days experiments, we evaluated the plant growth variables, TPH concentration, soil dehydrogenase activity (DHA) that is reflective of the rhizosphere microbial activity, and the aerobic bacterial count. The results suggest that the TPH concentration in first condition (0.80%) could not bring about a significant recovery of plant growth. The plant growth observed in first condition was equal to that observed in the case of the upper limit TPH concentration used in our previous study. However, under the second condition, it is suggested that the addition of zeolite could increase plant growth, which can in turn improve the rhizodegradation effect.